Hydrocarbons

ABSTRACT

A method of removing hydrocarbon-based adherent, for example bitumen, from a solid substrate, for example tar sands comprises contacting the solid substrate which includes associated hydrocarbon-based adherent with a treatment formulation which includes a polymeric material which includes vinylalcohol and vinylacetate repeat units. The polymeric material may be a 70-95 mole % hydrolysed polyvinylalcohol.

This invention relates to hydrocarbons and particularly, although not exclusively, relates to removal of hydrocarbon-based adherents from a solid substrate.

There are a number of environments in which hydrocarbon-based materials, such as oil, adhere to mineral or metal surfaces. In these cases, the effective separation of the oil from the substrate, i.e. cleaning, can be an important part of further use or disposal of the substrate or the adherent.

Cleaning agents prepare and clean surfaces by interacting with adherents, altering their properties, and minimizing the tendency of the adherent to adhere to the surface. The chemistry of cleaning agents and surface treatments is highly advanced. Liquid cleaning formulations include degreasers, strippers, passivators, etchants, solutions and additives for cleaning and surface preparation. They are used to remove adherents (grease or oil) from surfaces such as industrial equipment or mechanical components.

Formulations for cleaning are often, but not exclusively, water based. They may include the following:

Strong alkalis: These are extremely caustic solutions used to dissolve greases and certain minerals. Strong alkalis are known to boost the performance of other additives (e.g. chelants and builders described below) as well as to improve the dissolution rates for some minerals and scale deposits. Examples include sodium hydroxide and potassium hydroxide.

Medium strength alkalis: These are moderately caustic solutions used to remove fats, oils, and some paints and lacquers. Sodium carbonate is an example.

Mild alkalis: These are slightly basic solutions used for water softening and light cleaning. Sodium bicarbonate and water soluble silicates are examples.

Strong acids: These are highly corrosive materials used to dissolve hard mineral deposits. Examples include sulphuric, hydrochloric and hydrofluoric acids.

Mild acids: These are slightly corrosive materials used to soften water and control mineral deposition. Examples include acetic, citric and gluconic acid.

Solvents: This category includes a variety of substances used to dissolve grease and oil without the hazards of corrosivity. Solvents for cleaning consist of compounds such as alcohols, chlorinated hydrocarbons, or terpenes. Solvents may replace the water in a formulation or be additives in water based formulations (mutual solvents). Examples include acetone, isopropyl alcohol, d-limonene and 2-butoxyethanol. Solvents may be flammable, toxic and difficult to handle in practice.

Surfactants: These fall into the general category of detergents that are widely used as household cleaners. There is a multitude of examples including soaps (natural surfactants) and synthetic detergents. Some surfactants are used to emulsify fats, oils, and greases and are effective at lifting organic adherents from surfaces. Other surfactants (demulsifiers) are designed to release solid materials from the body of slurries, composed of highly viscous emulsions, within which the solid materials may be entrained. Subject to type and concentration, surfactants can be highly effective. However, many surfactants are associated with environmental disadvantages. Also, when used to clean oil from surfaces, surfactants can bind the oil so strongly into emulsions that the oil cannot be recovered and converted into gasoline or even disposed of safely and in a cost effective manner.

Dispersants: This category of additives shows behaviour that is closely related to that of surfactants. Their activity may be milder than that of surfactants or detergents. They are designed to prevent adherents, once cleaned from surfaces, from re-agglomerating rapidly. This slow agglomeration provides benefits such as stability or enhanced biodegradation due to increases in the surface area of contaminant droplets. Examples include polyelectrolytes, polysaccharide gums or lignosulphonates.

Chelants, Sequestrants and Builders: These are organic substances, which are soluble or miscible with water, that are added to formulations to minimize harmful characteristics of hardness ions such as cationic forms of calcium, magnesium, iron and manganese. Such ions interfere with the cleaning ability of primary active components (detergents and surfactants), effectively consuming them and making them unavailable to act on the surfaces to be cleaned. Chelants, sequestrants and builders ‘bind up’ the harmful ions converting them into harmless configurations where they cannot consume the primary active components. Examples of substances in this category include polydentate ligands such as ethylene diamine tetraacetic acid, polyphosphonates, gluconates, polyols, glucoheptonates, thioglycollic acid, water soluble silicates and certain carbonates. The addition of such materials to formulations adds cost and design complexity.

Preservatives: These are incorporated in formulations to protect soaps and detergents against the natural effects of aging such as decay, discoloration, oxidation and bacterial degradation. Examples of preservatives include butylated hydroxytoluene, methyl or propyl paraben and water soluble compounds of tin.

Biologically Active Materials: These are materials, such as enzymes and bacterial cultures, designed to remove adhering organic materials through the digestion of such adherents leading to the conversion of contaminants to carbon dioxide, water or other acceptable substances. Such biologically active materials may be damaging to the environment and are subject to strict regulation.

The above adherents, and/or combinations thereof, have functions and features that can be optimized for specific applications. They may be highly effective but their extreme behaviour may bring associated disadvantages. For example, it may be preferable to clean oil from a material using a treatment fluid that provides only a modest level of cleaning, perhaps leaving a lubricating proportion of oil on the surface, but allows easy dehydration of the dispersion and recovery of the oil, as opposed to using an aggressive detergent that binds oil to water practically irreversibly.

In order to be effective both for removal of hydrocarbon based adherents from a solid substrate and for downstream processing of the removed material, a treatment formulation requires a balance of the following properties:

(i) Detergency—this involves reducing surface tension between the adherent and the solid substrate and emulsification of the removed adherent.

(ii) Dispersion—this involves reducing and maintaining a size of removed adherent in a liquid.

(iii) Emulsion breaking or dehydration—this involves separation of adherent, solid substrate and/or water emulsions.

Most cleaning products have been developed to have strong performance in one of areas (i), (ii) or (iii). For example, a combination of detergency and emulsion breaking is rare and normally mutually exclusive—i.e. the factors which increase detergency tend to act against subsequent separation of adherent, solid substrate and/or water.

Specific processes which require removal of hydrocarbons from a solid substrate and subsequent isolation and/or recovery of the hydrocarbons include cleaning bitumen from oil sands and processing oil in CHOPS (Cold Heavy Oil Production with Sand) processes. These are described further below.

Oil sands, alternatively called tar sand or bituminous sands, are composed of bitumen, quartz, aluminosilicates, clays, water and trace minerals. The proportions of these constituents varies from deposit to deposit but commonly oil sand will be approximately 75%-85% inorganic materials (sand, clay and minerals), 3%-6% water and a bitumen content ranging from 10% to about 20%. Bitumen, alternatively called unconventional oil or crude bitumen is petroleum that exists in a semi-solid or solid phase in natural deposits. Bitumen has an API gravity lower than 10 degrees, which equates to a density greater than water at 15.56° C. Bitumen densities at 15.56° C. fall in the range 1.00 g/cm³ to 1.03 g/cm³, more commonly 1.005 g/cm³ to 1.015 g/cm³. The viscosities of bitumen, at 20° C., fall in the range 10,000 cP to 10,000,000 cP at 25° C., more commonly 20,000 cP to 1,000,000 cP.

Oil sands may be extracted from the earth's crust by a number of methods including mining, the use of steam (steam assisted gravity drainage), solvents and the direct application of heat (THAI, electrical etc.).

After excavation by a mining process, it is common to treat the extracted oil sand with hot water, optionally containing a caustic material (soluble bicarbonates, caustic soda, caustic potash etc). After treatment with hot water and the optional caustic material, the resulting slurry is commonly piped to an extraction plant, alternatively called a frothing plant, where the slurry is allowed to separate assisted by gravity and agitation. During separation, air bubbles, originally entrained in the bitumen, adhere to the bitumen droplets to create a ‘bitumen froth’, which floats to the top of separation vessels, and is skimmed from the top. The separation may be optionally enhanced by bubbling gases through the slurry. This cleaning process leads to approximately 75% of the bitumen being extracted from the oil sand. The extracted bitumen froth, at this stage, is still contaminated with water and residual sand and its composition is approximately 60% petroleum, 20% solids and 30% water. The caustic materials, used in the process, have high alkalinity and may chemically modify the solids, contributing to the formation of fine clay particles or militating against the further removal of such solid material. In addition, the process leaves a significant amount of oil in a watery phase (referred to as the “middling”) below the froth and a bottom layer comprising sand and silt may also contain some oil.

It is desirable to make the overall extraction process safer and more effective, to extract greater than 75% of the bitumen and also facilitate the reduction in the solids content of the bitumen froth extracted by skimming.

In the CHOPS process (Cold Heavy Oil Production with Sand), oil is simply pumped out of the sands via conventional wellbores equipped with subsurface pumps, commonly progressing cavity pumps or mechanical beam pumps. This only works well in areas where the oil is mobile enough to flow, which typically means that the oil viscosity is in the region 10,000 cP to 150,000 cP at 25° C., commonly 20,000 cP to 70,000 cP. Such oil may be classified as bitumen if its API gravity is less than 10 degrees, or simply flowable heavy oil if its API gravity is greater than 10 degrees.

In the CHOPS process, oil is produced with proportions of sand that vary between 5% and 40% throughout the lifetime of the production period, and water contents that vary between 1% and 90%, commonly 5% to 50%. Once produced, oil is removed from the sand and water by gravity separation in a heated processing vessel, often close to the wellhead. The separated oil, sand and water are collected, usually by road tanker. The separated oil is processed and sold, and the water and sand are treated as waste with related disposal costs. The sand contains somewhere between 5 and 15% oil.

It is desirable to reduce the amount of oil left in the sand and therefore achieve a greater oil recovery rate.

It is an object of the present invention to address the above described problems and/or to provide a method of treatment which optimises all three of the above described properties (i.e. detergency, dispersion and emulsion breaking) while being environmentally acceptable.

According to a first aspect of the invention, there is provided a method of removing hydrocarbon-based adherent from a solid substrate, the method comprising contacting a solid substrate which includes associated hydrocarbon-based adherent with a treatment formulation which includes a polymeric material which includes vinylalcohol and vinylacetate repeat units.

Said hydrocarbon-based adherent is preferably an oil. It is preferably a crude oil which in the context of the present specification includes tar (heavy crude oil), obtained from tar sands and bitumen. It may be a light oil having an API in the range 30 to 70, for example 30 to 45. It may be a heavy oil. For example, the oil may have an API gravity less than 30°, suitably less than 25°, preferably less than 20°. In some cases, the API gravity may be less than 15°. Where the oil is a bitumen, the API may be less than 10°.

In general terms, the solid substrate may comprise a naturally-occurring substrate or may be man-made. For example, it may comprise siliceous materials, sands, aluminosilicates or clays; or it may comprise a metallic surface, for example of a pipe or receptacle.

Preferably, said treatment formulation has an Interfacial Tension (IFT) measured against a sample of the hydrocarbon-based adherent to be removed in the range 2 to 20 mN/m.

Since some hydrocarbon-based adherents, for example oils, are too viscous for IFT to be conveniently measured, the sample of oil is diluted with toluene at a ratio of oil:toluene of 75:25. The IFT referred to is therefore based on the diluted material. IFT may be measured by a standard method as described in Example 6 hereinafter.

Said IFT may be at least 6 mN/m, suitably at least 7 mN/m, preferably at least 8 mN/m, more preferably at least 9 mN/m. The IFT may be less than 18 mN/m, suitably less than 16 mN/m, preferably less than 14 mN/m, more preferably less than 12 mN/m, especially less than 10 mN/m. Preferably, the IFT is in the range 8 to 14 mN/m, especially 9 to 12 mN/m.

The actual concentration of said polymeric material in said treatment formulation may be linked to the IFT of the adherent to be treated in the method. For example, if the concentration of the polymeric material exceeds 0.3 wt %, further increases in concentration lead to minimal changes in IFT. Also, as concentrations decrease from 0.3 wt % to zero, the IFTs progress exponentially back to the values for untreated adherent. The actual concentration selected is suitably one which gives an IFT in the range 5 mN/m to 16 mN/m and a surface tension (air/water) between 60 mN/m and 40 mN/m. Suitably, the IFT for adherents to be treated is about half that measured against water, in the absence of said polymeric material.

Said treatment formulation may have a surface tension (in the absence of any oil) at 25° C., preferably in the range 35 to 66 mN/m, more preferably in the range 40 to 65 mN/m.

Said treatment formulation suitably comprises water and said polymeric material, wherein suitably said polymeric material affects the IFT of the treatment formulation in relation to said adherent and/or modifies the water so it has the IFT as described herein.

Said treatment formulation is suitably aqueous. It suitably comprises at least 80 wt %, preferably at least 90 wt %, more preferably at least 95 wt %, especially at least 98 wt % water. It may include 99.9 wt % or less of water.

Said treatment formulation suitably includes at least 0.1 wt %, preferably at least 0.2 wt %, more preferably at least 0.4 wt % of said polymeric material. It may include less than 2 wt %, preferably less than 1%, more preferably less than 0.5 wt %.

Said treatment formulation suitably includes 96 to 99.9 wt % of water, 0.1 to 1 wt % of said polymeric material and 0 to 3 wt % of other additives, such as biocides or corrosion inhibitors. The amount of other additives may be less than 2.5 wt %, suitably less than 2.0 wt %, preferably less than 1 wt %. Preferably, said treatment formulation includes 98 to 99.9 wt % of water, 0.1 to 0.5 wt % of said polymeric material and 0 to 2 wt % of other additives.

Water for use in the treatment formulation may be derived from any convenient source. It may be potable water, surface water, sea water, aquifer water, deionised production water and filtered water derived from any of the aforementioned sources. Said water is preferably a brine, for example sea water or is derived from a brine such as sea water. The references to the amounts of water herein suitably refer to water inclusive of its components, e.g. naturally occurring components such as found in sea water. Water may include up to 6 wt % dissolved salts but suitably includes less than 4 wt %, 2 wt % or 1 wt % or less of dissolved salts which are naturally occurring in the water.

Said polymeric material is preferably wholly soluble in treatment formulation at the concentration used in the method and at 25° C. Said polymeric material is preferably soluble to at least 1 wt % at 25° C. in de-ionized water.

Said polymeric materials is preferably non-ionic.

Said polymeric material may have a weight average molecular weight (Mw) of less than 200,000, suitably less than 150,000, preferably less than 100,000, more preferably less than 50,000. The Mw may be at least 5,000, preferably at least 10,000. The Mw may be in the range 5,000 to 25,000, more preferably in the range 10,000 to 25,000.

In some situations, wherein said adherent is a bitumen having an API of less than 10°, the preferred polymeric material for said treatment formulation may have a higher molecular weight compared to when higher API oils are being treated. For example, when the API is less than 10°, the weight average molecular weight may be greater than 50,000, or greater than 75,000 or greater than 100,000. The molecular weight may be less than 300,000 or less than 250,000. In addition, when the API is less than 10°, the concentration of the polymeric material may be greater than when high API oils are being treated. For example, when the API is less than 10°, the treatment formulation may include at least 0.5 wt %, for example 0.5 to 3 wt % or 1 to 2 wt % of said polymeric material.

Weight average molecular weight may be measured by light scattering, small angle neutron scattering x-ray scattering or sedimentation velocity. The viscosity of the specified aqueous solution of the polymeric material may be assessed by Japanese Standards Association (JSA) JIS K6726 using a Type B viscometer. Alternatively, viscosity may be measured using other standard methods. For example, any laboratory rotational viscometer may be used such as an Anton Paar MCR300.

The viscosity of a 4 wt % aqueous solution of the polymeric material at 20° C. may be at least 2.0 cP, preferably at least 2.5 cP. The viscosity may be less than 6 cP, preferably less than 5 cP, more preferably less than 4 cP. The viscosity is preferably in the range 2 to 4 cP. The aforementioned viscosity suitably refers to a situation for oils other than bitumen being treated. For bitumen, the viscosity (and the molecular weight as discussed above) of the polymeric material used in the treatment formulation may be higher.

Said polymeric material preferably includes a saturated, preferably aliphatic, hydrocarbon backbone.

Said polymeric material is preferably a random copolymer (as opposed to a block copolymer).

Said polymeric material may include more than two different repeat units. However, preferably it includes no more than two different types of repeat units.

In said polymeric material, the mole % of vinylalcohol repeat units divided by the mole % of vinylacetate repeat units may be in the range 1.5 to 19, preferably in the range 2 to 15, more preferably in the range 4 to 12.

Said polymeric material suitably comprises at least 50 mole %, preferably at least 60 mole %, more preferably at least 70 mole %, especially at least 80 mole % of vinylalcohol repeat units. It may comprise less than 99 mole %, suitably less than 95 mole %, preferably less than 91 mole % of vinylalcohol repeat units. Said polymeric material suitably comprises 60 to 99 mole %, preferably 80 to 95 mole %, more preferably 85 to 95 mole %, especially 80 to 91 mole % of vinylalcohol repeat units.

Said polymeric material preferably includes vinylacetate repeat units. It may include at least 2 mole %, preferably at least 5 mole %, more preferably at least 7 mole %, especially at least 9 mole % of vinylacetate repeat units. It may comprise 30 mole % or less, or 20 mole % or less of vinylacetate repeat units. Said polymeric material preferably comprises 9 to 20 mole % of vinylacetate repeat units.

Said polymeric material is preferably not cross-linked.

Suitably, the sum of the mole % of vinylalcohol and vinylacetate repeat units in said polymeric material is at least 80 mole %, preferably at least 90 mole %, more preferably at least 95 mole %, especially at least 99 mole %.

Said polymeric material preferably comprises 70-95 mole %, more preferably 80 to 95 mole %, especially 85 to 91 mole % hydrolysed polyvinylalcohol.

Said treatment formulation may be at a temperature of at least ambient temperature immediately prior to contact with said solid substrate.

Said treatment formulation suitably has a viscosity at 25° C. and 100s⁻¹ of greater than 0.98 cP, suitably greater than 1 cP, preferably greater than 1.2 cP, especially greater than 1.5 cP. Said treatment formulation preferably has a viscosity under the conditions described of not greater than 10 cP, preferably of 5 cP or less, more preferably of 2 cP or less.

Said treatment formulation may have a pH in the range 5 to 9, for example 6 to 8. It may have about a neutral pH.

In the method of the first aspect, said solid substrate and/or said treatment formulation may be agitated after contact so as to mix the treatment formulation and solid substrate.

The method of the first aspect preferably includes separating treatment formulation which includes adherent (e.g. oil) from solid substrate with which it was previously associated. The treatment formulation and adherent suitably form a dispersion which comprises the adherent dispersed in water of the treatment formulation. This dispersion may be separated from the solid substrate by any suitable means.

The method of the first aspect preferably includes a step of selecting said dispersion and treating it to produce a first part and a second part. Said first part preferably comprises water and said first polymeric material, wherein the concentration of adherent in said first part is less than the concentration in said dispersion. The ratio of the concentration in said dispersion divided by the concentration in said first part may be at least 2, 3 or 4. Said second part preferably comprises said adherent, wherein the concentration of water in said second part is less than the concentration of water in the dispersion. Thus, the treatment to produce said first and second parts suitably comprises the dehydration of said dispersion to produce a first part which includes less adherent than in said dispersion and a second part which includes more adherent than in said dispersion.

In one embodiment, the method of the first aspect may be used to enhance production-oil recovery. The method may comprise extracting a mass of solid substrate containing an adherent which is a crude oil from the ground. The mass is preferably naturally occurring in the ground. It preferably includes particulates in combination with oil both of which suitably occur together naturally as a mass in the ground. In particular, the particulates preferably occur naturally as particulates in the ground. Preferably, the particulates are indigenous in the ground. They are suitably different to any particulates used or formed during an intervention (e.g. drilling) by an operator. The mass is preferably derived from (e.g. it is initially present in) a region of ground which is at least 5 m, 10 m, 15 m or 50 m from an imaginary vertical line (or a real vertical line where the mass is removed from the ground via a wellbore) which defines a position wherein the mass is removed from the ground.

Said mass suitably includes at least 3 wt %, preferably at least 5 wt %, more preferably at least 8 wt % of crude oil. It may include less than 40 wt % of crude oil. It may include at least 3 wt % of water. Said mass preferably includes at least 5 wt % of naturally-occurring particulate material, for example indigenous particulates as described. Particulates as described may comprise gravel, sand, silt and/or clays. Said mass preferably includes at least some sand.

In the method of the first embodiment, the mass is suitably extracted as described and is contacted with treatment formulation at the surface to remove oil from the solids (e.g. particulates) included in the mass.

A first example of the first embodiment may comprise removing bitumen from oil sands, obtained for example by mining. Such oil sands may comprise a mass which includes 75 to 85 wt % of inorganic materials (e.g. sand, clay and/or minerals); it may include 3 to 6 wt % water; and it may include 10 to 20 wt % of bitumen. The bitumen by definition has an API gravity of less than 10°.

After removal of the oil sands, the oil sands may be contacted with said treatment formulation, and suitably agitated. A slurry is suitably formed which may be allowed to separate, optionally assisted by gravity and agitation. The separation preferably includes forming a bitumen froth, which may optionally be enhanced by bubbling a gas through the slurry. Use of the treatment formulation enhances separation of the bitumen from other components of the slurry.

A second example of the first embodiment may comprise a CHOPS process. In the process, the mass extracted from the ground suitably comprises oil and sand; it is preferably extracted via a wellbore, suitably under the motive of a surface pump, for example a progressing cavity pump or mechanical beam pump. The oil is suitably mobile enough to flow. It may have a viscosity in the range 10,000 cP to 150,000 cP at 25° C. and, more commonly, in the range 20,000 cP to 70,000 cP.

The mass may include 5 to 40 wt % sand, 1 to 90 wt % water (more commonly 5 to 50 wt % water) and 5 to 94 wt % oil, (more commonly 50 to 90 wt %).

After extraction the mass may be introduced into a separation vessel. The treatment formulation may be associated with the mass in the separation vessel and may facilitate removal and/or isolation of the oil from the sand.

In a second embodiment, the method of the first aspect may be used to remove adherent, for example oil, from a solid substrate primarily to decontaminate the solid substrate, rather than primarily recover oil for subsequent use. Decontamination of the solid substrate may facilitate disposal of the solid substrate in accordance with legislation or other appropriate commercial practices.

In the second embodiment, the method may include disposing of the solid substrate after the level of oil contained in it has been reduced in the method. The liquid removed from the solid substrate may be treated to facilitate separation of an oil-rich part and a water-rich part.

A first example of the second embodiment may comprise treating waste sand from a CHOPS well with said treatment formulation. In a second example, oil-containing sludge in a receptacle, for example a tank may be contacted with said treatment formulation to facilitate mobilisation of the sludge and extraction and/or isolation of an oil-rich part therefrom. In a further example, the method may be used to clean a conduit, for example a pipe or wellbore, and/or remove oil therefrom.

The effectiveness of a formulation as described herein may, where applicable, be illustrated using a Batch Extraction Unit (BEU) in a BEU test which may be used to determine the distribution of oil in various phases after treatment and be used to compare the efficacy of different treatment.

In a further embodiment, a treatment formulation may include said polymeric material having any of the features described above. 70-95% mole % hydrolysed polyvinylalcohol is especially preferred. The polymeric material may suitably have a molecular weight (Mw) in the range 10,000 to 200,000 and/or as described above. The treatment formulation may include 10 to 40 wt % (preferably 20 to 40 wt %) water, 0.1 to 2 wt % (preferably 0.1 to 1.0 wt %) of said polymeric material and 59.9 wt % to 89.9 wt % (preferably 59.9 to 79.9 wt %) of a light oil, suitably having an API in the range 30 to 70°, for example 30 to 45°. The light oil may be selected from vegetable oil, diesel oil, kerosene, canola oil and olive oil. The aforementioned components of the treatment formulation are suitably blended so that the oil is dispersed in the aqueous phase, wherein the aqueous phase suitably contains said polymeric material. The formulation may be used to remove heavy oil (e.g. oil having an API lower than that of said light oil). Said heavy oil may have an API of less than 30°, suitably less than 25° or less than 20°.

The light oil in the formulation is believed to act as a cleaning agent in use. It is believed the formulation works because the dispersed light oil droplets have a high surface area, through which the heavy oil adherent is consumed, perhaps by simple dilution. In some situations, it may be desirable to stabilise the formulations, using surfactants or fine solids; however, if aggressive shearing is used in preparation of the formulations, the formulations may, in any event, be relatively stable.

The formulation described may be used to remove heavy oil as described from a solid substrate. For example, sludge, for example a sand-based “pit sludge” (e.g. containing 10 to 20 wt % of water, 35 to 55 wt % hydrocarbons and 25 to 55 wt % solids) may be treated with the formulation, for example mixed with it. After treatment, the solids are found to be relatively clean. There may also be an associated water phase and a separate oil phase which includes oil from the sludge dissolved in the light oil.

According to a second aspect, there is provided a method of recovering oil from a subterranean formation which comprises:

(i) extracting a mass comprising oil mixed with indigenous sand from the formulation;

(ii) contacting the mass with a treatment formulation;

(iii) separating the sand from oil and components of the treatment formulation to produce two parts, one being sand-rich and the other comprising oil and components of the treatment formulation;

(iv) treating the dispersion to produce an oil-rich part; and separating the oil-rich and water-rich parts from one another, for example by delivery of the parts into separate receptacles or conduits.

The method of the second aspect may include any feature of the method of the first aspect mutatis mutandis.

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a plot of interfacial tension (IFT) v. polymer concentration in a treatment formulation for two oils;

FIG. 2 is a plot of results from Amott Cell tests on an oil;

FIG. 3 is a plot illustrating dehydration rate for specified dispersions.

The following material is referred to hereinafter:

Polyvinylalcohol I—a polyvinylalcohol containing only hydroxyl and acetyl functional groups, with a degree of hydrolysis of 89% and a molecular weight in the range 15,000 g/mol to 18,000 g/mol.

It has been found that an aqueous solution of polyvinylalcohol I provides an excellent balance of detergency, dispersion and emulsion breaking properties meaning that it may be used in a range of treatments in which hydrocarbon-based adherents may be removed from solid substrates. Hereinafter, the properties of the polyvinylalcohol are discussed, followed by various uses of the material.

The detergency of aqueous formulations of polyvinylalcohol I may be illustrated by assessing interfacial tension (IFT) and wettability as discussed in Examples 1 and 2.

EXAMPLE 1 Reduction in Interfacial Tension (IFT)

Materials and Equipment:

-   -   a. Solid polyvinylalcohol I     -   b. Oil I having an API gravity of 13.3 degrees     -   c. Oil II having an API gravity of 7.6 degrees     -   d. Tap water     -   e. Toluene     -   f. Kruss DSA 100 drop shape analyser equipped with a ‘J needle’.

0.5 gram of polyvinylalcohol I was dissolved in 100 ml of tap water to make a treatment formulation containing 0.5 wt % polymer. A 10 g sample of oil I was mixed intimately with 3.3 g of toluene to create a flowable oil/toluene blend. The interfacial tension between the oil/toluene blend and the treatment formulation was determined, at 25° C., using the Kruss DSA drop shape analyser.

The process was first repeated using progressively decreasing proportions of the polymer in the treatment fluid, and again using oil II.

FIG. 1 shows a plot of interfacial tension, v. polymer concentration in the treatment formulation, for both oils I and II. The data demonstrates that, for both oils, IFT values fall by only a factor of 2 as the concentration of the polymer in solution increases from 0% to 0.5%. By comparison, had suitable surfactants been used, the IFT values would have fallen to below 10⁻² mN/m. We take the moderate proportion of IFT reduction with the treatment formulation to indicate a level of detergency less than would be expected for a preferred surfactant.

EXAMPLE 2 Assessing Wettability Modification Using an Amott Cell

-   -   a. Solid polyvinylalcohol I     -   b. Oil III having a shear rate independent viscosity at 20° C.         of 45,000 cP     -   c. Brine having a total dissolved solids content of 20,000 mg/I     -   d. Sand having a mean particle size of 200 μm and composed of         98% silica     -   e. Amott Cell

5 grams of polyvinylalcohol I was dissolved in 1 litre of brine to make a treatment formulation. A compacted blend containing 20 g of oil III with 2 g of brine and 11 g sand was prepared for Amott cell wettability testing. Oil separation tests were performed, over a period of 16 days at 20° C., with the Amott cell, using standard Amott cell procedures.

The process was repeated replacing the treatment formulation with polymer free brine to define a baseline.

FIG. 2 shows the proportion of oil detached from the compacted blend as a function of elapsed time. We see that, after the sixteen day incubation period, the treatment fluid was observed to cause the release of over 44% of the original oil, whilst the polymer free brine released only 17%. The brine is seen to reach its maximum oil recovery level after only two days, but the treatment formulation detachment of oil under these static conditions indicates that the wettability of the sand surface is changed in the presence of the treatment formulation towards a more water-wet character.

The dispersion forming ability of aqueous formulations of polyvinylalcohol I may be illustrated by Examples 3 and 4.

EXAMPLE 3 Dispersion Formation with Multiple Oils

Materials and Equipment:

-   -   a. Solid polyvinylalcohol I     -   b. Oil IV having a shear rate independent viscosity at 20° C. of         145,000 cP     -   c. Oil V having a shear rate independent viscosity at 20° C. of         39,000 cP     -   d. Oil VI having a shear rate independent viscosity at 20° C. of         19,700 cP     -   e. Oil VII having a shear rate independent viscosity at 20° C.         of 2,700 cP     -   f. Tap water     -   g. Anton Paar MCR 300 rheometer equipped with parallel plate         sensor and a gap size of 1 mm

1 gram of polyvinylalcohol was dissolved in 200 ml of tap water to make a treatment formulation. 30 grams of the treatment formulation was added to 250 ml screw top jar and to it was added 70 grams of oil IV. The jar was sealed and the blend was shaken by hand 50 times to create a dispersion of oil droplets in a water based treatment fluid (dispersion 1). Samples of the dispersion were taken for viscosity determination using the Anton Paar rheometer at 20° C.

The process was repeated using oils V, VI and VII to make dispersions 2, 3 and 4 respectively.

Table 1 shows measured values of apparent viscosity at selected wall shear rates (flow curve), along with the corresponding shear rate independent viscosities for the three oils.

TABLE 1 Apparent Viscosities at Selected Wall Shear Rates (Flow Curves) Wall Apparent Viscosity cP Shear Oil Disper- Oil Disper- Oil Disper- Oil Disper- Rate 1/s IV sion 1 V sion 2 VI sion 3 VII sion 4 0.1 145,000 2030 39,000 2930 19,700 3182 2,700 2400 0.5 145,000 1138 39,000 1300 19,700 1270 2,700 928 1 145,000 915 39,000 928 19,700 801 2,700 600 5 145,000 444 39,000 527 19,700 293 2,700 250 10 145,000 345 39,000 370 19,700 237 2,700 204 50 145,000 230 39,000 180 19,700 161 2,700 125 100 145,000 200 39,000 127 19,700 130 2,700 100

Table 1 indicates that the apparent viscosities of the dispersions reduce to a single flow curve i.e. the dispersion characteristics are standardised regardless of the original oil viscosity.

EXAMPLE 4 Brine Tolerance

Materials and Equipment:

-   -   a. Solid polyvinylalcohol I     -   b. Oil VIII having a shear rate independent viscosity at 20° C.         of 6,700 cP     -   c. Oil IX having a shear rate independent viscosity at 20° C. of         82,000 cP     -   d. Brine 1 composed of 889 ppm total dissolved solids and 60 ppm         total hardness ions     -   e. Brine 2 composes of 26,380 ppm total dissolved solids and 110         ppm total hardness ions     -   f. Brine 3 composed of 39,946 ppm total dissolved solids and 860         ppm total hardness ions     -   g. Brine 4 composed of 78,720 ppm total dissolved solids and         1920 ppm total hardness ions     -   h. Anton Paar MCR 300 rheometer equipped with parallel plate         sensor and a gap size of 1 mm

1 gram of polyvinylalcohol I was dissolved in 200 ml of brine 1 to make a treatment formulation. 30 grams of the treatment formulation was added to 250 ml screw top jar and to it was added 70 grams of Oil VIII. The jar was sealed and the blend was shaken by hand 50 times to create a dispersion of oil droplets in a water based treatment fluid. Samples of the dispersion were taken for viscosity determination using the Anton Paar rheometer at 20° C.

The process was repeated using brines 2 to 4 in combination with oil VIII and then again with brines 1 to 4 in combination with oil IX.

Table 2 shows the rheological properties of dispersions made with different brines.

TABLE 2 Apparent Viscosities at Selected Wall Shear Rates (Flow Curves) in Different Brines Wall Apparent Viscosity cP Shear Oil Oil Rate 1/s VIII Brine 1 Brine 2 Brine 3 Brine 4 IX Brine 1 Brine 2 Brine 3 Brine 4 0.1 6,700 2400 2980 1777 1500 82,000 2000 2133 2170 2456 0.5 6,700 1138 1200 1059 1200 82,000 1010 928 940 1035 1 6,700 911 873 739 755 82,000 700 789 111 800 5 6,700 400 367 356 414 82,000 367 455 500 470 10 6,700 360 288 311 350 82,000 300 325 304 451 50 6,700 146 127 139 187 82,000 188 211 220 165 100 6,700 84 100 121 133 82,000 150 145 150 80

Table 2 indicates that, regardless of the brine salinity or concentration of total hardness ions, the apparent viscosities of the dispersions reduce to a single flow curve which is consistent with the data for dispersions in table 1.

The emulsion breaking properties of aqueous formulations of polyvinylalcohol I may be illustrated by assessing dehydration of the formulations over time as described in Example 5.

EXAMPLE 5 Kinetic Plots of Dehydration Vs Time at 35° C.

Materials and Equipment:

-   -   a. Solid polyvinylalcohol I     -   b. Oil X having shear rate independent viscosity at 20° C. of         10,000 cP     -   c. Oil XI having shear rate independent viscosity at 20° C. of         725 cP     -   d. Tap water     -   e. 100 ml graduated cylinder

1 gram of polyvinylalcohol I was dissolved in 200 ml of tap water to make a treatment formulation. 35 grams of the treatment formulation was added to 250 ml screw top jar and to it was added 81.7 grams of Oil X. The jar was sealed and the blend was shaken by hand 50 times to create a dispersion of oil droplets in a water based treatment fluid. This process resulted in the formation of 116.7 grams of a dispersion that contained exactly 30% by weight of the treatment fluid. Exactly 100 g of dispersion was transferred to the graduated measuring cylinder, which was incubated at 35° C. and the volume of separated water recorded as it evolved with time. The proportion of water retained in the oil phase was calculated by difference.

The process was repeated using oil XI.

FIG. 3 shows plots of water retained in the oil vs time for both oil tested. In both cases, separation is rapid, with over 90% of the treatment fluid being released within 24 hours. By comparison, with many surfactants, a substantial proportion of the oil may have been entrained practically irreversibly in the dispersion.

IFT as described herein may be measured as described in Example 6.

EXAMPLE 6 General Method of Determination of Interfacial Tension by Kruss Pendant Drop Method

The method is generally in accordance with Shi-Yow Lin, Li-Jen Chen, Jia-Wen Xyu and Wei-Jiunn Wangi, Langmuir 1996, 11, 4159-4166 4159. It was undertaken at 25° C. However, since oils are too viscous to pass through the needle, the oil was diluted with toluene prior to being tested at an oil:toluene ratio of 75:25.

A Kruss DSA1000 Surface Tensiometer was used to measure IFT between two liquids at ambient temperature with a J-Needle. In the method, a fluid drop, of a certain shape, is created hanging from an upturned needle while suspended in an optical cell containing another fluid and mathematical equations are used to calculate the Interfacial Tension between those two fluids. The procedure used was as follows:

-   -   (i) The angle of inclination of the prism (Tilt) was turned to         0°.     -   (ii) A Hamilton glass syringe was filed with no more than 0.4 ml         of the fluid to be tested and it was ensured there was no air         entrapped in the syringe.     -   (iii) The J-Needle was screwed onto the end of the syringe and         the syringe was pushed into the syringe holder on the syringe         unit ensuring there was a gap between the glass flange of the         syringe and the uppermost clip of the syringe holder and that         the end of the plunger fits into the syringe unit.     -   iv) The zoom function on the unit was adjusted so that the         needle occupies approximately 10% of the screen.     -   v) The Optical Glass Cell was slid under the needle and the cell         was completely filled with the fluid to be tested. The sample         table was raised until the needle was just touching the bottom         of the cell.     -   vi) The image was focused.     -   vii) With the dosing mode set as ‘Continuous’ a dosing rate of         20 microlitres/minute was input. The syringe unit then started         to push test fluid down through the needle and a drop started to         form and could be seen on the screen. The ideal shape for a drop         image is the image of a drop just about to drop off the needle.         However with viscous fluids it is very difficult to determine         the ideal shape as the drop tends to form a spherical shape due         to the weight acting down of the embedded phase. Initial         investigations into this method have shown that very large drops         are required to get consistent accurate results. For optimum         results the drop image needs to fill as much of the window as         possible hence the zoom may have to be adjusted.     -   viii) The drop was developed at the low dosing rate to an         appropriate size and then the image was captured.     -   ix) The software was then used to calculate the Interfacial         Tension between the two fluids.

Thus, it will be appreciated from the above that the treatment formulations described have an excellent balance of detergency, dispersion and emulsion breaking properties. Such a balance in properties may be highly beneficial in the processes described herein.

In general terms, materials to be treated may comprise a solid substrate in combination with a hydrocarbon-based adherent. Hydrocarbons may be a conventional crude oil removed from tar sands that have become immobile through cooling. The original viscosities of the hydrocarbons may be in the range 10 cP to 10 million cP at 25° C. Most likely the viscosities of the hydrocarbons will be in the range 1000 cP to 500,000 cP at 25° C. and preferably below 100,000 cP. The definition of hydrocarbon may be extended to include petroleum products that have aged, through processes such as oxidation or biodegradation, or be contaminated with inorganic or organic substances such as clays, rust particles, trace mineral, resins or asphaltenes. Hydrocarbons may be sludges taken from storage tanks or produced by refinery processes. A solid substrate may be siliceous materials, sand, aluminosilicates, clays or cuttings from the oilwell drilling process. They may be metallic surfaces of pipes, storage tanks, rail cars or other receptacles. Alternatively, the solid substrate may exist as discrete particles having mean number average particle sizes in the range 5 microns to 500 microns as determined by laser light scattering methods.

In a first application, a treatment formulation as described may be used in removing bitumen from oil sands.

An aqueous formulation of polyvinylalcohol I as described may be used in place of the hot water/caustic treatment fluid used in oil sands treatment as described in the introduction of this specification. Thus, the method may comprise contacting oil sands, for example obtained in a mining process, with said treatment formulation, suitably to produce a slurry. The slurry may be delivered to a frothing plant to effect at least partial separation of the oil from the sands. The method may include separating a froth containing oil from the sand. Use of the aqueous formulation may make the overall extraction process safer and more effective, leading to greater than 75% of the bitumen being extracted and also facilitate the reduction in the solids content of the bitumen froth extracted by skimming. Advantageously, the formulation readily removes the bitumen from the oil sands by reducing interfacial tension between the bitumen and oil sands and a dispersion is formed. The formulation may also reduce the amount of oil in the middling and/or bottom layer by dispersing and displacing it. Nonetheless, the dispersion is not irreversibly formed and, accordingly, can readily be broken to isolate the bitumen from the aqueous phase.

In a second application, a treatment formulation as described may be used in processing oil in a CHOPS (Cold Heavy Oil Production with Sand) process.

A treatment formulation comprising polyvinylalcohol I as described may be added to the separation vessel in the CHOPS treatment described in the introduction of this specification to facilitate removal of the oil from the sand and its dispersion in an aqueous phase which may subsequently be dehydrated to isolate the oil. In some embodiments. the formulation of polyvinylalcohol I may additionally contain emulsion breaking chemicals of types conventionally used for dewatering oil. Thus, use of the treatment formulation may increase the oil recovery rate.

In a third application, a treatment formulation as described may be used in oil recovery and waste remediation at landfill sites.

Waste sand taken from CHOPS wells is transported to landfill sites. In most cases mechanical separators (centrifuges or decanters) are used to treat some of the sand and recover some of the residual oil (as described in the second application above). However, even after mechanical separation, waste sand contains a low level of residual oil.

Landfill sites are categorised according to the hazard rating of waste they can receive. Consequently, hydrocarbon content, flash point, and proportion of leachable substances (volatile aromatics benzene, toluene, ethyl-benzene, and xylene) are factors in establishing the disposal restrictions on waste material. It is advantageous therefore if waste materials have low levels of residual hydrocarbon so they can conform to less restrictive disposal requirements.

A pre-soak with a treatment formulation comprising polyvinylalcohol I, immediately prior to mechanical separation, may enable a greater quantity of oil to be recovered and a less restrictive disposal classification to be achieved.

In a fourth application, a treatment formulation as described may be used in sludge mobilisation.

Regardless of the oil production method, hydrocarbon containing materials may be stored in tanks and pits for some time. Also, the hydrocarbon containing materials may be transported in metal tanks on rail cars or in oil tankers. The continued use of such vessels leads to the build up of sludge due to the settling of solids suspended in the oil. These sludges are difficult to handle and often need to be manually removed. This involves working in confined spaces; an activity which carries safety risks from accidents or the inhalation of toxic gases. A treatment formulation comprising polyvinylalcohol may be used to mobilise sludge and facilitate extraction with much less manual intervention. Benefits may lead to improvements in the discharge of wash-water and the minimisation of cost and complexity of waste disposal. The neutral pH of the treatment formulation may be a further benefit. This cleaning activity may support the cleaning systems already built into the facilities, such as jet washing. The formulation may additionally include detergents and scale control agents or demulsifiers.

In other applications, the advantageous balance of properties of the treatment formulation may be used to remove (and preferably subsequently isolate) oil from contaminated surfaces to, for example, maintain operability, remove hazards prior to maintenance and repair and, in some cases, prevent cross-contamination of products. Thus, treatment formulation as described may be used in cleaning tanks, tankers, pipelines or industrial plant and machinery.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 

1-23. (canceled)
 24. A method of removing hydrocarbon-based adherent from a solid substrate, the method comprising contacting a solid substrate which includes associated hydrocarbon-based adherent with a treatment formulation which includes a polymeric material which includes vinylalcohol and vinylacetate repeat units.
 25. The method according to claim 24, wherein said hydrocarbon-based adherent is a heavy oil having an API gravity less than 30°, for example less than 10°.
 26. The method according to claim 24, wherein said solid substrate comprises a naturally-occurring substrate.
 27. The method according to claim 24, wherein said treatment formulation has an Interfacial Tension (IFT) measured against a sample of the hydrocarbon-based adherent to be removed in the range 2 to 20 mN/m; and/or a surface tension (in the absence of any oil) at 25° C. in the range 35 to 66 mN/m.
 28. The method according to claim 24, wherein said treatment formulation comprises at least 95 wt %, especially at least 98 wt %, water; and at least 0.1 wt % and less than 2 wt %, of said polymeric material.
 29. The method according to claim 24, wherein said polymeric material has a weight average molecular weight (Mw) of less than 200,000; and the Mw is at least 5,000.
 30. The method according to claim 24, wherein said adherent is a bitumen having an API of less than 10° and said polymeric material has a weight average molecular weight of greater than 50,000; and preferably less than 300,000.
 31. The method according to claim 24, wherein in said polymeric material the mole % of vinylalcohol repeat units divided by the mole % of vinylacetate repeat units is in the range 1.5 to
 19. 32. The method according to claim 24, wherein said polymeric material comprises at least 50 mole % of vinylalcohol repeat units; and at least 2 mole % of vinylacetate repeat units.
 33. The method according to claim 24, wherein said polymeric material comprises 80 to 95 mole % of vinylalcohol repeat units; and at least 5 mole % of vinylacetate repeat units.
 34. The method according to claim 24, wherein the sum of the mole % of vinylalcohol and vinylacetate repeat units in said polymeric material is at least 80 mole %.
 35. The method according to claim 24, wherein said polymeric material comprises 70-95 mole % hydrolysed polyvinylalcohol.
 36. The method according to claim 24, wherein said treatment formulation has a viscosity at 25° C. and 100 s⁻¹ of greater than 0.98 cP; and/or said treatment formulation has a pH in the range 5 to
 9. 37. The method according to claim 24, wherein said solid substrate and/or said treatment formulation are agitated after contact so as to mix the treatment formulation and solid substrate.
 38. The method according to claim 24, wherein the method comprises extracting a mass of solid substrate containing an adherent which is a crude oil from the ground wherein said mass includes at least 3 wt % of crude oil; at least 3 wt % of water; and at least 5 wt % of naturally-occurring particulate material which includes at least some sand.
 39. The method according to claim 24, wherein the mass is extracted and is contacted with treatment formulation at the surface to remove oil from the solids included in the mass.
 40. The method according to claim 24, which comprises removing bitumen from oil sands.
 41. The method according to claim 40, wherein said oil sands comprise a mass which includes 75 to 85 wt % of inorganic materials and 10 to 20 wt % of bitumen.
 42. The method according to claim 40, wherein after removal of the oil sands, the oil sands are contacted with said treatment formulation thereby to form a slurry which is allowed to separate and includes forming a bitumen froth.
 43. The method according to claim 24, wherein said method comprises a CHOPS process.
 44. The method according to claim 24, wherein said method comprises treating waste sand from a CHOPS well with said treatment formulation.
 45. A method of recovering oil from a subterranean formation which comprises: (i) extracting a mass comprising oil mixed with indigenous sand from the formulation; (ii) contacting the mass with a treatment formulation; (iii) separating the sand from oil and components of the treatment formulation to produce two parts, one being sand-rich and the other comprising oil and components of the treatment formulation; (iv) treating the dispersion to produce an oil-rich part; and separating the oil-rich and water-rich parts from one another, for example by delivery of the parts into separate receptacles or conduits. 